The present invention relates to an injection device for a diesel engine, and more particularly to a unit injector for high pressure injection for a diesel engine.
In recent years, a unit injector for a high pressure injector for high pressure injection for a diesel engine has been strongly desired in order to improve air pollution due to the diesel engine and reduce fuel consumption. For example, in Japanese Patent No. 2524657, there is suggested a high pressure unit fuel injector provided with a variable length hydraulic link, for controlling an injection timing, and an injection pressure control valve. The fuel injector achieves improved pressure control without adversely influencing a controlled amount of a timing fluid.
FIG. 4 is a cross sectional view of a fuel injector 50 for high pressure injection described in the publication. An upper plunger 51, subject to a drive force from a cam shaft (not shown), is closely arranged in a cylinder hole 53 in such a manner as to freely slide in a vertical direction due to an upward force by a spring 52. A timing chamber 55 capable of changing a volume is formed between a lower end of the upper plunger 51 and an intermediate plunger 54. A timing fluid 56 such as a fuel is supplied to the timing chamber 55 via a narrow timing fluid passage 59 formed in an injector barrel 58. The timing fluid 56 forms a hydraulic link between the intermediate plunger 54 and the lower plunger 61, and is preferably discharged under a certain condition via a first drain passage 62 formed in a direction of a central axis through the intermediate plunger 54. Further, the timing chamber 55 communicates with a compensation chamber 63 via a valve mechanism 70 in a bottom portion of the first drain passage 62. The valve mechanism 70 is held between the lower end portion of the intermediate plunger 54 and the upper end portion of the lower plunger 61 arranged within the compensation chamber 63. When the valve mechanism 70 is opened, the timing fluid 56 flows within the compensation chamber 63 from the timing chamber 55 via the first drain passage 62 and is discharged out of the fuel injector 50 via a second drain passage 64. The valve mechanism 70 controls a pressure of the timing fluid 56 within the timing chamber 55, and next, the pressure controls an upper limit of the injection pressure of the fuel and a timing of the injection. The valve mechanism 70 is normally closed by application of a force due to a timing spring 65 arranged within the compensation chamber 63 and a valve spring 66 arranged within the lower plunger 61. Further, the force of the timing spring 65 pulls up the lower plunger 61 and operates so that three plungers, comprising the lower plunger 61, the intermediate plunger 54, and the upper plunger 51, are integrated until a controlled amount and a timing in the next cycle start after a completion of the injection cycle. A supply of the timing fluid 56 to the timing chamber 55 is performed through the narrow timing fluid passage 59. The injection timing is changed in accordance with a supplied amount of the timing fluid 56. For example, when the supplied amount is much, the injection timing is quickened. The timing spring 65 moves the lower plunger 61 upwardly a degree sufficient to feed out the fuel to an injection chamber 73 adjacent to an injection nozzle 71.
Next, when the injection timing is established by the supply of the timing fluid 56 within the timing chamber 55, the injected fuel flows within the injection chamber 73 via a supply orifice 75 of a fuel supply passage 74. The injected fuel in the injection chamber 73 is accurately controlled in accordance with a known pressure/time principle. An amount of the injected fuel controlled in the above manner becomes a function of a total control time for fluid flow through the fuel supply passage 74 and a supply pressure, and the fuel supply passage 74 has a hydraulic property so as to give a control capacity having a desired pressure/time.
Here, when the upper plunger 51 is driven downwardly due to a rotation of the cam, the timing fluid 56 is returned through the timing fluid passage 59 until the timing fluid passage 59 is closed by the lower portion of the upper plunger 51. The timing fluid 56 is trapped between the intermediate plunger 54 and the upper plunger 51, so that a hydraulic link for integrally moving all three plunger elements toward the nozzle 71, disposed on the bottom portion of the injection chamber 73, is formed. During downward motion of three plunger elements, when the timing fluid pressure becomes more than a maximum predetermined pressure determined by a resultant force of the valve spring 66 and the timing spring 65, the valve mechanism 70 is opened, so that the timing fluid 56 is discharged from the timing chamber 55 through the first and second drain passage 62 and 64 so as to reduce a pressure to conform to a predetermined limit value. Then, the supply orifice 75 of the fuel supply passage 74 is closed when the lower plunger 61 moves downwardly, so that a control of a fuel amount is finished. Further the lower plunger 61 moves downwardly, thereby injecting the controlled fuel in the injection chamber 73 from a plurality of orifices in the injection nozzle 71 within the combustion chamber (not shown).
However, the valve mechanism 70 mentioned above has a complex structure, so that a highly accurate dimension, flatness and the like are required for parts thereof. Further, since the valve mechanism 70 controls the pressure of the timing fluid 56, there is a problem in that an amount of leakage is not fixed due to a temperature, a viscosity, and the like of the fluid, so that the pressure is not fixed.
Further, in the case wherein the injection timing is controlled by an amount (a volume) of the timing fluid 56 supplied within the timing chamber 55, the amount of the timing fluid 56 is controlled by a magnitude of the timing fluid passage 59 and the control time. In accordance with the present publication, since the timing fluid is supplied through the timing fluid passage 59 in the form of the narrow fixed orifice, the amount of the timing fluid 56 is changed by a kind, a temperature, or a viscosity of the fluid, so that the injection timing is not fixed. On the contrary, when making the timing fluid passage 59 greater in cross-section, a range of the injection timing is narrowed. Further, when making the control time long, the volume of the timing chamber 55 is increased, so that there is a problem in that the fuel injector 50 itself becomes large.
Further, when controlling a little amount of fuel under a low rotational speed or a no load operation, it is necessary to make the timing fluid passage 59 of the fixed orifice narrow; however, when making it narrow, the control time becomes long in the case of intending to suddenly increase the fuel, so that a response of the engine is delayed. Particularly, in a vehicle having a great load change applied to the engine, such as a construction machine and the like, it is a great disadvantage that the response of the engine is delayed. Further, in the narrow fixed orifice, a dispersion (i.e., statistical variance) of the diameter thereof increases a rate of a dispersion in an area of the orifice, and increases a dispersion in the injection timing and the volume of the fuel.
In addition, the fuel to the injection chamber 73 is supplied via the supply orifice 75 in the fuel supply passage 74. The supply orifice 75 is also required to be made narrow for controlling a little amount of fuel at a time of the low rotational speed or the no load operation. However, when being made narrow, the control time becomes long in the case of intending to suddenly increase the fuel, so that there is a problem that the response of the engine is delayed.
An object of the present invention is to provide a fuel injection device for a diesel engine for solving the problems mentioned above, comprising a high pressure injection unit for a diesel engine having a wide range of injection timing, little dispersion, and a good response. In accordance with a first invention of the present invention, there is provided a fuel injection device for a diesel engine comprising a cylindrical body, an upper plunger, closely inserted within a hole of the body, to slide in a vertical direction responsive to an applied force from a cam, an intermediate plunger arranged below the upper plunger in such a manner as to be coaxial with the upper plunger and forming a pressure chamber for a hydraulic link with respect to the upper plunger, a lower plunger arranged below the intermediate plunger in such a manner as to be brought into contact with the intermediate plunger, and an injection chamber provided in a lower end portion of the body in which a fuel stored in the injection chamber is discharged by the lower plunger upon receiving an applied force from the upper plunger via the hydraulic link and the intermediate plunger, the improvement comprising:
a passage, having a large cross-sectional area, formed in the body for supplying a pressurized oil to the pressure chamber, the intermediate plunger is adapted to vertically move in response to an oil pressure so as to make it possible to change a volume of the pressure chamber, and a timing spring, having an end in contact with the intermediate plunger and the other end in contact with the lower plunger, to vertically move the timing plunger in response to the pressure.
In accordance with the structure mentioned above, in the case of rotating under no load and at a low rotational speed, an oil under a low pressure is supplied to the pressure chamber via the passage, and a fuel under low pressure is supplied to the injection chamber. Accordingly, in a downward slide motion, only the intermediate plunger is initially slid downward without moving the lower plunger downward, so that it is possible to delay the injection timing.
Further, in the case that the diesel engine rotates In under a high load and at a high rotational speed, the it pressurized oil under high pressure is supplied to the pressure chamber via the passage, and a large amount of fuel under high pressure is supplied to the injection chamber. Accordingly, in the downward slide motion, both the intermediate plunger and the lower plunger are immediately slid downward, so that fuel can be injected to a combustion chamber from the injection chamber at an early timing without delaying the injection timing.
As mentioned above, it is possible to obtain a delayed timing and an early timing by a simple structure, so that a predetermined range of injection timing can be easily obtained. That is, an injection timing having a predetermined range can be obtained by a delayed predetermined injection timing due to a predetermined interval between the intermediate plunger and the lower plunger at a low rotational speed under no load and an early injection timing at a high rotational speed in a state that there is no interval between the timing plunger and the lower plunger due to the pressure acting on the timing plunger at a high load.
Further, since the oil pressure and the oil amount are supplied to the pressure chamber via the passage, it is possible to quickly move to the early injection timing, so that a response of the engine can be improved. Further, since the timing spring is brought into contact with the lower plunger and both of them commonly move downward, there is an advantage that the pressure within the pressure chamber is not abnormally increased.
In accordance with a second invention, there is provided a fuel injection device for a diesel engine as In recited in the first invention, wherein the timing plunger has a first hole connected to the pressure chamber at a center portion and a second hole communicated with the first hole and passing through the timing plunger in a lateral direction, and the second hole communicates with a discharge hole provided below the passage when the timing plunger moves downward so as to discharge fuel collected in the injection chamber by the lower plunger.
In accordance with the structure mentioned above, the pressurized oil in the pressure chamber is discharged via the first hole, the second hole and the discharge hole when the timing plunger moves downward so as to restrict a movement of the lower plunger. Accordingly, the lower plunger does not press the body too much, so that it is possible to prevent the lower plunger or the body from breaking.
In accordance with a third invention, there is provided a fuel injection device for a diesel engine for injecting a fuel supplied via a fuel supply passage and stored in an injection chamber by a lower plunger responsive to an applied force from a cam through an upper plunger via a hydraulic link and a timing plunger comprising: a branch supply passage having an end connected to the fuel supply passage and the other end connected to the injection chamber; a variable valve to allow fuel to flow within the branch supply passage from the fuel supply passage only in a direction of the injection chamber, to open at a pressure equal to or more than a predetermined pressure of the supplied fuel, and to change a passing area in response to a pressure of the fuel; and a spring for the variable valve to set a moving amount of the variable valve in response to the pressure of the fuel.
In accordance with the structure mentioned above, the high pressure fuel discharged from the fuel pump of the engine is quickly supplied to the injection chamber. Since the high pressure fuel supplied to the injection chamber is supplied to the injection chamber also from the variable valve within the branch supply passage in addition to the fuel supply passage, the fuel is collected in the injection chamber with a good response. Since a large amount of fuel supplied to the injection chamber is injected into a combustion chamber by a downward slide motion at a high pressure, it is possible to increase an output force without decrease of the rotational speed of the engine, and a fast speed and a good response can be obtained.
In accordance with a fourth invention, there is provided a fuel injection device for a diesel engine comprising a cylindrical body, an upper plunger, closely inserted within a hole of the body, to slide in a vertical direction in response to an applied force from a cam, an intermediate plunger arranged below the upper plunger in such a manner as to be coaxial with the upper plunger and forming a pressure chamber for a hydraulic link with respect to the upper plunger, a lower plunger arranged below the intermediate plunger in such a manner as to be brought into contact with the intermediate plunger, and an injection chamber provided in a lower end portion of the body, structured such as to discharge a fuel supplied via a fuel supply passage and stored in the injection chamber by the lower plunger subject to the force from the upper plunger via the hydraulic link and the intermediate plunger, the improvement comprising:
a passage, having a large cross-sectional area and formed in the body, for supplying a pressurized oil to the pressure chamber, the intermediate plunger vertically movable in response to an oil pressure so as to make it possible to change a volume of the pressure chamber, a timing spring having an end being brought into contact with the intermediate plunger and the other end being brought into contact with the lower plunger and vertically moving the intermediate plunger in response to the oil pressure, a branch supply passage having an end connected to the fuel supply passage and the other end connected to the injection chamber, a variable valve to allow fuel to flow within the branch supply passage from the fuel supply passage only in a direction of the injection chamber, to open at a pressure equal to or more than a predetermined pressure of the supplied fuel, and to change a passing area in response to a pressure of the fuel, and a spring for the variable valve setting a moving amount of the variable valve in response to a pressure of the fuel.
In accordance with the structure mentioned above, since the oil pressure and the oil amount are supplied to the pressure chamber via the passage for the pressurized oil, it is possible to quickly move to an early injection timing, so that a response of the engine can be improved. Further, since the oil pressure and the oil amount are supplied to the pressure chamber via the passage for the pressurized oil, no narrow hole is required, so that a variability of the injection timing is reduced. Since the device is constituted by a simple structure comprising the intermediate plunger, or timing plunger, the timing spring and the like, the device is not of a large size.
Further, since the high pressure fuel supplied to the injection chamber is supplied to the injection chamber also from the variable valve within the branch supply passage in addition to the fuel supply passage, the fuel is collected with a good response. Since a large amount of fuel supplied to the injection chamber is injected to the combustion chamber by a downward slide motion of the lower plunger, an output force can be increased without reduction of the rotational speed of the engine, and a fast speed and a good response can be obtained.